Axial piston pump

ABSTRACT

The invention relates to an axial piston swash plate pump, in particular for hydraulic systems, comprising a cylinder drum ( 1 ) which can be rotationally driven about an axis ( 15 ) in a pump housing ( 7 ), in which pistons ( 21 ) are arranged in an axially displaceable manner supporting, by means of the actuation end thereof ( 31 ) which is accessible from the outside of the cylinder drum ( 1 ), at least indirectly a swash plate ( 3 ), said swash plate being pivotable to the desired angles of inclination with respect to the axis ( 15 ) in order to adjust the stroke of the piston ( 21 ) and also the fluid system pressure generated thereby. Said swash plate ( 3 ) is mounted, for the pivotable movements thereof, on the pump housing ( 7 ) by means of a swash plate bearing ( 39, 41 ); characterized in that a supply device ( 5 ), which enables a fluid which is at a system pressure to travel at least to the swash plate bearing ( 39, 41 ), is provided.

The invention relates to an axial piston pump in a swashplate design, in particular for hydraulic systems, with a cylinder drum which can be driven to rotate about an axis in a pump housing and in which pistons are disposed in an axially movable manner, the actuating end of the pistons, which is accessible outside of the cylinder drum, at least indirectly abutting a swashplate, which can be pivoted to the desired angle of inclination relative to the axis to adjust the stroke of the piston, and hence the thereby-generated fluid system pressure, wherein, for its pivoting movements, the swashplate is mounted by means of a swashplate bearing on the pump housing.

Axial piston pumps in a swashplate design are prior art. They are widely used for supplying hydraulic fluid to consumers such as operating cylinders, hydraulic motors, and the like. Axial piston pumps of the above-cited type, in which the inclination of the swashplate can be adjusted relative to the axis, are distinguished relative to axial piston pumps with a fixed swashplate, which are also known, by an improved energy balance during operation. Whereas pumps with a fixed swashplate, as a constant pump with a given drive speed, always convey a constant volumetric flow of the fluid even if no energy is required by aggregates actuated by hydraulic fluid and consequently the flow resistance in the hydraulic circuit must be overcome even during idling, which expends drive energy that does not supply any useful energy, the displacement volume is adjustable to zero since the inclination of the swashplate can be adjusted, and the required drive energy can be minimized. An axial piston pump of the initially-cited type is disclosed in DE 44 15 510 C1.

DE 25 31 616 A describes an axial piston machine with a housing in which a driven shaft is mounted that is connected for conjoint rotation with a cylinder drum. Pistons are disposed in the cylinder drum so as to be axially movable, wherein the pistons each abut a swashplate with a sliding shoe arranged on an actuating end. A hold-down plate ensures that the sliding shoes are in constant contact with the swashplate. The flat swashplate is a part of a cradle which pivotably abuts a bearing shell. The cradle is pivoted by controlling hydraulic fluid pressure in two opposing pressure chambers disposed below the cradle which enables the piston stroke to be adjusted. Two axial, peripherally opposing support tubes disposed in the interior of the housing have an inner channel for conducting a hydraulic fluid into the pressure chambers below the cradle, wherein the respective support tube is pressed by a set of cup springs against a seat formed by a ball cap on a support part of the cradle. Fluid can therefore be reliably supplied to and removed from the pressure chambers.

Based on this prior art, the object of the invention is to provide an axial piston pump with a swashplate that can be adjusted to the desired angle of inclination and which is characterized by particularly high reliability of operation, even during long-term operation.

According to one aspect of the invention, this object is achieved according to patent claim 1 in that a supply device is provided, by means of which the fluid under system pressure at least reaches the swashplate bearing. Pressurized lubrication is available for the swashplate bearing, by means of which the fluid, such as the hydraulic fluid used in hydraulic systems, can be supplied through holes formed in the swashplate and areas of the bearing corresponding to channels which are subject to a load during operation. Even during long-term operation with a high number of adjustment cycles and/or with swashplate pivoting movements occurring at a high frequency, proper functioning is therefore ensured along with corresponding high operational reliability.

According to another aspect of the invention, the object addressed by the invention is achieved according to claim 2 in that a presure device is provided which keeps the swashplate in contact with the swashplate bearing. When the pump is operating while the swashplate is adjusted to a pivoted position in which a volumetric flow and corresponding system pressure are generated, the system pressure acts via the pistons on the swashplate such that it is held in its bearing. In a depressurized system when the pump is not operating or the swashplate is not pivoted relative to the axis, i.e., is in a home position and there is no system pressure, no force exerted by pressure via the pistons acts on the swashplate. By means of the pressing device provided according to the invention, the swashplate is secured against falling out of its bearing even during these operating situations such that the pump can be reliably operated even when adjusted to zero delivery.

In particularly advantageous exemplary embodiments, the supply device forms a component of the pressing device and has a tube that forms a fluid connection between a fluid path of the pump housing that conveys system pressure, and the swashplate. By means of suitable lubrication channels formed in the swashplate, a desirable supply of lubricant to the relevant bearing sites can be implemented.

In a particularly advantageous manner, the pressing device can have an energy store, preferably in the form of a spring arrangement, for generating the contact pressure holding the swashplate on the swashplate bearing.

In particularly advantageous exemplary embodiments, the tube is connected to the swashplate by means of an articulation enabling pivoting movements of the swashplate relative to the tube, and forming a fluid connection. Consequently, the tube does not have to be connected to the pump in a pivotable manner, and the connection of the tube to the housing can have a simple design.

In a particularly advantageous manner, a disk spring set can be disposed between the end of the tube facing away from the swashplate and a part of the pump housing conducting system pressure, the disk spring set serving as an energy store and pretensioning the tube for transmitting the contact force against the articulation which is provided at the transition between the swashplate and the associated, other end of the tube.

The articulation can be designed in the manner of a ball joint and have a ball head located at one end of the tube and a connecting piece located on the swashplate in which a ball socket is formed which receives the ball head and in which a fluid passage is provided which continues the fluid path of the tube.

It is particularly advantageous for the arrangement to be configured such that the tube extends parallel to the axis adjacent to the cylinder drum, and such that the connecting piece with the ball socket, which receives the ball head, is arranged on a lateral projection of the swashplate.

In the following, the invention will be explained in detail with reference to an exemplary embodiment depicted in the drawings. In the figures:

FIG. 1 shows a side view of a schematically simplified representation in which are depicted only the cylinder drum, the swashplate and an articulated tube serving as the supply and pressing device of an exemplary embodiment of the axial piston pump according to the invention;

FIG. 2 shows a longitudinal section of an exemplary embodiment of the axial piston pump;

FIG. 3 shows an enlarged and exploded, perspective oblique view of the articulated tube serving as a supply and pressing device; and

FIG. 4 shows a perspective oblique view of the separately depicted swashplate of the exemplary embodiment.

Of the exemplary embodiment to be described, FIG. 1 shows a simplified representation of only one rotating cylinder drum 1 with an associated, pivotable swashplate 3 and an articulated pipe 5 that is disposed adjacent to the cylinder drum 1 and forms a supply and pressing device. The pump housing designated by 7 in FIG. 2 is omitted in FIG. 1. In said FIG. 1, the swashplate is depicted at a pivoted angle which corresponds to the maximum delivery volume with a correspondingly high system pressure. As shown in FIG. 2, the pump housing 7 has a top part 9 at the top in the drawing, and a bottom part 11. A driveshaft 13 for the cylinder drum 1 is mounted in the top part 9 in a cylinder roller bearing 16 for the rotary movement about the axis designated by 15, and the driveshaft 13 is mounted in the bottom part 11 by means of a slide bearing 17. The cylinder chambers 19 of the cylinder 21 with the pistons 21 guided therein (only one cylinder chamber 19 is visible in the sectional plane in FIG. 2) are, at the bottom the cylinder in the drawing, in contact with a control ring 24 which abuts the bottom housing part 11 and has control openings 25 which form fluid inlets from the suction side 27 and outlets to the pressure side 29.

During the rotary movement of the cylinder 1, the pistons 21 glide across the sliding shoe 31 on the sliding surface 33 which is located on the bottom side of the swashplate 30. The sliding shoes 31 are connected in the manner of a ball joint to the top side of the piston, wherein an oil hole 35 penetrating from the respective cylinder chamber 19 to the sliding surface 33 enables an access for fluid such as hydraulic fluid for lubricating the sliding surface 33.

To adjust the delivery volume, the swashplate 3 is adjustable about a pivot axis 37 which lies in the plane of the sliding surface 33 of the swashplate 3. This pivot axis 37 is defined by the swashplate bearing between the swashplate 3 and top part 9. At the top part 9, the swashplate bearing has a plastic bearing shell 39 against which the swashplate 3 is guided with a dome-shaped sliding surface 41. For the passage of the drive shaft 13, a through-hole 49 is formed in the sliding surface 41 in the swashplate 3 which expands conically upward (see in particular FIG. 4). On both sides next to the opening 43, guide rails 45 are provided as a part of the swashplate bearing, which project out of the sliding surface 41. For the pivoting movement of the swashplate 3 about the pivot axis 37, the side of the swashplate 3 on the left in FIG. 2 is screwed to a swiveling lever which extends parallel to the axis 15 next to the cylinder drum 1 and, at its bottom end 49 in FIG. 2, is movable in the direction running perpendicular to the plane of the drawing in order to instigate a corresponding pivoting movement of the swashplate 3 about the pivot axis 37. On the associated side of the swashplate 3, the pivoting lever 47 is screwed into an inner thread located in a hole 57.

The articulated tube 5 which is shown separately with its associated components in FIG. 1, and which forms a component of a supply and pressing device as shown in FIGS. 1 and 2, is arranged on the side next to the cylinder drum 1 in the direction running parallel to the axis 15. With its bottom end in FIGS. 1 and 2, the articulated tube 5 is mounted in a seat 53 (see FIG. 1) in a connecting block 55 on the bottom housing part 11, wherein the seat 53 enables the articulated tube 5 to be displaced axially. The block 55 contains a connecting channel 57 (FIG. 1) leading to the pressure side 29 which terminates in the seat 53 of the articulated tube 5. The top end of the articulated tube 5 is articulated to the swashplate 3 by a connecting piece 58 which is disposed laterally outside of the sliding surface on the bottom side of the swashplate 3. The articulation is realized by a type of ball joint and, at the top end of the articulated tube 5, has a ball head 59 that is accommodated in a ball socket 51 of the connecting piece 58. The articulated tube 5 is clamped against the swashplate 3 by the connecting piece 58. For this purpose, a disk spring set 63 is arranged between the bottom end of the articulated tube 5 and the floor of the seat 53. A sealing ring 65 (see FIG. 3) forms a seal between the outside of the articulated tube 5 and the seat 53. A fluid passage 67 in the connecting piece 58 continues the fluid connection to the pressure side 29 beyond the mouth of the pipe at the ball joint 59 to the swashplate 3. The screwed connection between the connecting piece 58 and swashplate 3 is sealed by sealing rings 69 (FIG. 3). Lubrication channels 71, 73, 75 formed within the swashplate 3 connect to the passage 67 of the connecting piece 58, of which the vertical channels 75 (see FIGS. 2 and 4) for supplying lubricant to the swashplate bearing terminate at the relevant sites of the sliding surface 41. A leakage volumetric flow resulting from the supply of fluid serving as the lubricant to the swashplate bearing is discharged from the pump housing 7 in a conventional manner through a leakage oil line, for example to a tank.

When the pump is operating while the swashplate is in a pivoted position during which a volumetric flow is conveyed and a system pressure is generated, the swashplate 3 is held in the swashplate bearing by the system pressure acting via the pistons 21 on the swashplate 3.

No force exerted by pressure acts on the swashplate 3 when the swashplate 3 is pivoted back, so that the pump is operating in idle with zero delivery and no system pressure is being generated, or when the pump is turned off. Given a vertical installation position of the pump, the danger exists that the swashplate 3 can fall out of the swashplate bearing. With the invention, this danger is avoided in that the articulated pipe 5, in addition to the function of supplying lubricant to the swashplate bearing, forms a pressing device by means of the pretension generated by the disk spring set 63, and holds the swashplate against the pivot bearing under contact force. 

1. An axial piston pump in a swashplate design, in particular for hydraulic systems, with a cylinder drum (1) which can be driven to rotate about an axis (15) in a pump housing (7) and in which pistons (21) are disposed in an axially displaceable manner, the actuating end (31) of the pistons is accessible outside of the cylinder drum (1), at least indirectly abutting a swashplate (3), which can be pivoted to the desired angle of inclination relative to the axis (15) to adjust the stroke of the piston (21), and hence the thereby-generated fluid system pressure, wherein for its pivoting movements, the swashplate (3) is mounted by means of a swashplate bearing (39, 41) on the pump housing, characterized in that a supply device (5) is provided by means of which the fluid under system pressure at least reaches the swashplate bearing (39, 41).
 2. An axial piston pump in a swashplate design, in particular for hydraulic systems, with a cylinder drum (1) which can be driven to rotate about an axis (15) in a pump housing (7) and in which pistons (21) are disposed in an axially movable manner, the actuating end (31) of the pistons is accessible outside of the cylinder drum (1) at least indirectly abutting a swashplate (3) which can be pivoted to the desired angle of inclination relative to the axis (15) to adjust the stroke of the piston (21), and hence the thereby-generated fluid system pressure, wherein for its pivoting movements, the swashplate (3) is mounted by means of a swashplate bearing (39, 41) on the pump housing, characterized in that a pressing device (5) is provided which holds the swashplate (3) in contact with the swashplate bearing (39, 41).
 3. The axial piston pump according to claim 1, characterized in that the supply device forms a component of the pressing device and has a tube (5) that forms a fluid connection between a fluid path (57) of the pump housing (7) that conveys system pressure, and the swashplate (3), and transmits a contact force to the swashplate (3) which holds the swashplate to the swashplate bearing (39, 41).
 4. The axial piston pump according to claim 1, characterized in that the compression device (5) has an energy store, preferably in the form of a spring arrangement (63), for generating the contact pressure holding the swashplate (3) on the swashplate bearing (39, 41).
 5. The axial piston pump according to claim 1, characterized in that the tube (5) is connected to the swashplate (3) by means of an articulation (59, 61) for enabling pivoting movements of the swashplate relative to the tube (5) and forming a fluid connection.
 6. The axial piston pump according to claim 1, characterized in that a disk spring set (63) is disposed between the end of the tube (5) facing away from the swashplate (3) and a part (55) of the pump housing (7) conducting system pressure, the disk spring set pretensioning the tube (5) for transmitting the contact force against the articulation (59, 61) which is provided at the transition between the swashplate (3) and the associated, other end of the tube (5).
 7. The axial piston pump according to claim 1, characterized in that the articulation is designed in the manner of a ball joint and has a ball head (59) located at one end of the tube (5) and a connecting piece (58) located on the swashplate (3) in which a ball socket (61) is formed which receives the ball head (59) and in which a fluid passage (67) is provided which continues the fluid path of the tube (5).
 8. The axial piston pump according to claim 1, characterized in that the tube (5) extends parallel to the axis (15) adjacent to the cylinder drum (1), and the connecting piece (58) with the ball socket (61), which receives the ball head (59), is arranged on a part of the swashplate (3) lying on the side of the sliding surface (33).
 9. The axial piston pump according to claim 1, characterized in that one side of the swashplate (3) is connected to a pivoting lever (37) for the pivoting movement of the swashplate (3) about a pivot axis (37), and the pivoting lever extends parallel to the axis (15) of the cylinder drum (1), and one end (49) of the pivoting lever can be displaced in a direction running perpendicular to the axis (15).
 10. The axial piston pump according to claim 1, characterized in that a pressing device (5) is provided which holds the swashplate (3) in contact with the swashplate bearing (39, 41). 